1. Field of the Invention
The invention relates to novel C.sub.24 and C.sub.34 diesters and the method of their preparation.
2. Brief Description of the Prior Art
It has been known for some time that aliphatic aldehydes and ketones react with hydrogen peroxide to form hydroperoxide compounds of the type RCHOH(OOH). The hydroperoxide formed from cyclohexanone and hydrogen peroxide has been shown to have the simple structure: ##STR1## and also the structure: ##STR2## which may break down in solution to give cyclohexanone and 1,1-dihydroperoxycyclohexanone. It has been shown that the solid peroxide of structure (II) when shaken with an aqueous solution of ferrous sulfate yields mainly hexanoic and 1,12-dodecanedioic acids and cyclohexanone.
The reaction of ferrous salts with peroxides derived from cyclic ketones has occasioned considerable interest, largely the result of the formation of open chain products, particularly those having double the number of carbon atoms present in the original ketones: such products bear close resemblance to those obtained from 1-hydroperoxy-1-alkylcycloalkanones. Replacement of ferrous sulfate with ferrous chloride leads to a sharp decrease in the yield of C.sub.12 diacid. This result is not surprising in view of French Patent No. 1,152,642, which claims that good yields of 6-chlorohexanoic acid may be produced under these conditions. Conditions which lead to decreased yields include high temperatures, poor mixing and the use of reduced proportions or concentrations of hydrogen peroxide.
As described in U.S. Pat. No. 2,601,223, Brown has achieved high conversions of the C.sub.12 diacid using methanol solutions of the peroxides, derived from the oxidation of cyclohexanol. Cyclic ketones other than cyclohexanone have been found to react in a similar manner, although yields of corresponding dicarboxyclic acids have been found to be generally lower: 2-chloro-1-hydroperoxycyclohexanol gave dichlorododecanedioic acid; cyclopentanone, sebacic acid, and 4-methylcyclohexanone give 4,9-dimethyl dodecanedioic acid.
U.S. Pat. No. 2,757,192 has disclosed that the introduction of conjugated dienes such as butadiene, isoprene, and chloroprene into the reaction mixture of ketone and hydrogen peroxide leads to the formation of long chain unsaturated dicarboxylic acids, with the addition of butadiene giving rise to the C.sub.20 acids including: EQU HOOC [CH.sub.2 ].sub.5 CH.sub.2 CH=CH--CH.sub.2 CH.sub.2 [CH.sub.2 ].sub.5 COOH (III)
It has also been shown that the conjugated dienes may be replaced by dimethyl maleate giving rise to a hexaester formed by dimerization of the radical: ##STR3## (See J. Org. Chem., 23, 1066 (1958)).
U.S. Pat. No. 3,984,462 describes the process for producing dodecanedioic acid dimethyl ester. This process is a modification of the above described technology by substituting methanol as the solvent. The use of methanol as solvent for higher conversion to the C.sub.12 acid has been reported by Brown in J.Am. Chem. Soc., 77, 1756 (1955). The process comprises the reaction of cyclohexanone with methanol and hydrogen peroxide in the presence of an acid catalyst to produce methoxycyclohexylhydroperoxide and subsequent reaction with ferrous sulfate. The methyl esters produced may be separated by distillation and subsequently saponified to recover the corresponding diacids which are then separated by fractional crystallization of the linear and branched products.
Japanese Patents Nos. 78 59,618, and 78 63,309 describe a process where butadiene is added in the second step to produce C.sub.20 dimethyl esters.